This back door came from a 424 Princess Deluxe or 429 Starlet that I parted out years ago.
I believe other than color it is the same on the 434 Concerto.
This type is fastened to the cabinet using 3 spring steel clips on the top edge.

I recently sorted the dozens of Rock-ola back door panels of this type that I have accumulated over the years.
I had marked many of them when I parted out the machines - using that and other information I now have a good idea what sizes fit which machines.

The metal panel offered here measures 28.875 inches long.
The full width including the lip which is hidden when installed is 11.500 inches.
I am measuring to the nearest 1/8 of an inch.

If there is any doubt in your mind measure the opening on your machine before ordering.

Depending on model, the Rock-ola Parts Catalogs name this item as the
Back Door Assembly, the Back Door & Cushion Assembly, the Back Door & Bumper Assembly or the Back Door Riveting Assembly.

It is in good condition but the paint is not perfect and may need to be cleaned or touched up.